Eureka

Yeah I found it : yesterday I was looking for how to add tab on the upper page ( or tabbar) like on this blog

Not sidebar, there is a plenty of non sense plugin, javascript and so which add your page on your side bar. The solution : in wp-admin Pages> add a new page. Of course depending on the theme you use, the theme must display it. Everything is in the theme.

I was nearly switching to Joomla to own the tabbar. Now just one thing I still don’t know how to a post to under a certain page